Computer use such as surfing the Internet may be hazardous as criminals have infested it by malicious software (malware). Antivirus control is crucial in avoiding damage caused by the malware. However, antivirus software may produce false alarms. Consequently, further sophistication of the antivirus software is desirable. The present application deals especially with worms (=a self-replicating stand-alone malware computer program) and Trojans (=a non-self-replicating stand-alone malware computer program), but not with viruses (=a non-self-replicating non-stand-alone malware computer program, which replicates itself by inserting a copy of itself into another computer program, data file or boot sector of a hard drive, for example)